Integrating Systems for Liquid/Substrate Characterization and Functional Printing

Gallium-Indium alloys are recently applied in fabricating soft devices, such as stretchable sensors, electric circuits, micro pumps and optics. Its printability demonstrates the possibility for a wide extension of the application. Current fabrication methods are inefficient when printing is most handled manually, and are highly dependent on material properties. There is need for a fast way to characterize material properties, and to functionally print the given shape on the substrate. This paper presents the construction of an efficiently integrated system with optical imaging and functional printing for Gallium-Indium alloys. The imaging section allows for characterization of material properties to fast and accurately determine printing parameters in printing section. A new algorithm, which extends generalized Hough Transform, is designed to determine the contact angle of sessile drops by fitting the shape based on Bashforth-Adams equation. The results are later applied in determination of featured geometry in printing. The algorithm shows relatively low errors in profiling the sessile drop shapes. However, the results are not stable for 5% of test pictures, and thus revisions are still needed. In addition, functional printing is finalized with a direct writing module and a friendly user interface. A series of the state-of-the-art algorithms are adopted in image analysis and controlling. Test printing shows its workability, flexibility and accordance to the previous work. The integrated system presents a solution for both accuracy and efficiency in Gallium-Indium alloy printing

Understanding the Dynamics of Cellulose Dissolved in an Ionic Liquid Solvent Under Shear and Extensional Flows

Financiado para publicación en acceso aberto: Universidade de Vigo/CISUGIonic liquids (ILs) hold great potential as solvents to dissolve, recycle, and regenerate cellulosic fabrics, but the dissolved cellulose material system requires greater study in conditions relevant to fiber spinning processes, especially characterization of nonlinear shear and extensional flows. To address this gap, we aimed to disentangle the effects of the temperature, cellulose concentration, and degree of polymerization (DOP) on the shear and extensional flows of cellulose dissolved in an IL. We have studied the behavior of cellulose from two sources, fabric and filter paper, dissolved in 1-ethyl-3-methylimidazolium acetate ([C2C1Im][OAc]) over a range of temperatures (25 to 80 °C) and concentrations (up to 4%) that cover both semidilute and entangled regimes. The linear viscoelastic (LVE) response was measured using small-amplitude oscillatory shear techniques, and the results were unified by reducing the temperature, concentration, and DOP onto a single master curve using time superposition techniques. The shear rheological data were further fitted to a fractional Maxwell liquid (FML) model and were found to satisfy the Cox–Merz rule within the measurement range. Meanwhile, the material response in the non-LVE (NLVE) regime at large strains and strain rates has special relevance for spinning processes. We quantified the NLVE behavior using steady shear flow tests alongside uniaxial extension using a customized capillary breakup extensional rheometer. The results for both shear and extensional NLVE responses were described by the Rolie-Poly model to account for flow-dependent relaxation times and nonmonotonic viscosity evolution with strain rates in an extensional flow, which primarily arise from complex polymer interactions at high concentrations. The physically interpretable model fitting parameters were further compared to describe differences in material response to different flow types at varying temperatures, concentrations, and DOP. Finally, the fitting parameters from the FML and Rolie-Poly models were connected under the same superposition framework to provide a comprehensive description within the wide measured parameter window for the flow and handling of cellulose in [C2C1Im][OAc] in both linear and nonlinear regimes.Xunta de Galicia | Ref. ED481B-2018/06

Rapid in-situ quantification of rheo-optic evolution for cellulose spinning in ionic solvents

It is critical to monitor the structural evolution during deformation of complex fluids for the optimization of many manufacturing processes, including textile spinning. However, in situ measurements in a textile spinning process suffer from paucity of non-destructive instruments and interpretations of the measured data. In this work, kinetic and rheo-optic properties of a cellulose/ionic liquid solution were measured simultaneously while fibers were regenerated in aqueous media from a miniature wet spinline equipped with a customized polarized microscope. This system enables to control key spinning parameters, while capturing and processing the geometrical and structural information of the spun fiber in a real-time manner. We identified complex flow kinematics of a deformed fiber during the coagulation process via feature tracking methods, and visualized its morphology and birefringent responses before and during regeneration at varying draw ratios and residence time. Meanwhile, a three-dimensional physical rheological model was applied to describe the non-linear viscoelastic behavior in a complex wet-spinning process incorporating both shear and extensional flows. We subsequently compared the birefringent responses of fibers under coagulation with the transient orientation inferred from the rheological model, and identified a superposed structure-optic relationship under varying spinning conditions. Such structural characterizations inferred from the flow dynamics of spinning dopes are readily connected with key mechanical properties of fully-regenerated fibers, thus enabling to predict the spinning performance in a non-destructive protocol.Comment: 28 pages, 6 figure

Rapid in situ quantification of rheo-optic evolution for cellulose spinning in ionic solvents

It is critical to monitor the structural evolution of complex fluids for optimal manufacturing performance, including textile spinning. However, in situ measurements in a textile-spinning process suffer from the paucity of non-destructive instruments and interpretations of the measured data. In this work, kinetic and rheo-optic properties of a cellulose/ionic liquid solution are measured simultaneously while fibers are regenerated in aqueous media from a model wet-spinning process via a customized polarized microscope. This system enables to capture key geometrical and structural information of the fiber under spinning at varying draw ratios and residence time, including the flow kinematics extracted from feature tracking, and the flow-induced morphology and birefringent responses. A physics-oriented rheological model is applied to connect the kinematic and structural measurements in a wet-spinning process incorporating both shear and extensional flows. The birefringent responses of fibers under coagulation are compared with an orientation factor incorporated in the constitutive model, from which a superposed structure-optic relationship under varying spinning conditions is identified. Such structural characterizations inferred from the flow dynamics of spinning dopes exhibit strong connections with the mechanical properties of the fully-regenerated fibers, thus enabling to predict the spinning performance in a non-destructive protocol.Agencia Estatal de Investigación | Ref. PRE2020-093158Agencia Estatal de Investigación | Ref. RYC2021-033826-IUniversidade de Vigo/CISU

Rethinking Normalization Methods in Federated Learning

Federated learning (FL) is a popular distributed learning framework that can reduce privacy risks by not explicitly sharing private data. In this work, we explicitly uncover external covariate shift problem in FL, which is caused by the independent local training processes on different devices. We demonstrate that external covariate shifts will lead to the obliteration of some devices' contributions to the global model. Further, we show that normalization layers are indispensable in FL since their inherited properties can alleviate the problem of obliterating some devices' contributions. However, recent works have shown that batch normalization, which is one of the standard components in many deep neural networks, will incur accuracy drop of the global model in FL. The essential reason for the failure of batch normalization in FL is poorly studied. We unveil that external covariate shift is the key reason why batch normalization is ineffective in FL. We also show that layer normalization is a better choice in FL which can mitigate the external covariate shift and improve the performance of the global model. We conduct experiments on CIFAR10 under non-IID settings. The results demonstrate that models with layer normalization converge fastest and achieve the best or comparable accuracy for three different model architectures.Comment: Submitted to DistributedML'22 worksho

The retropharyngeal reduction plate for atlantoaxial dislocation: a finite element analysis

Objective: To investigate the biomechanical properties of the retropharyngeal reduction plate by comparing the traditional posterior pedicle screw-rod fixation by finite element analysis.Methods: Two three-dimensional finite element digital models of the retropharyngeal reduction plate and posterior pedicle screw-rod fixation were constructed and validated based on the DICOM (Digital Imaging and Communications in Medicine) data from C1 to C4. The biomechanical finite element analysis values of two internal fixations were measured and calculated under different conditions, including flexion, extension, bending, and rotation.Results: In addition to the backward extension, there was no significant difference in the maximum von Mises stress between the retropharyngeal reduction plate and posterior pedicle screw fixation under other movement conditions. The retropharyngeal reduction plate has a more uniform distribution under different conditions, such as flexion, extension, bending, and rotation. The stress tolerance of the two internal fixations was basically consistent in flexion, extension, left bending, and right bending.Conclusion: The retropharyngeal reduction plate has a relatively good biomechanical stability without obvious stress concentration under different movement conditions. It shows potential as a fixation option for the treatment of atlantoaxial dislocation

Biomechanical evaluation of different posterior fixation techniques for treating thoracolumbar burst fractures of osteoporosis old patients: a finite element analysis

Objective: To investigate the biomechanical characteristics of different posterior fixation techniques in treatment of osteoporotic thoracolumbar burst fractures by finite element analysis.Methods: The Dicom format images of T10-L5 segments were obtained from CT scanning of a volunteer, and transferred to the Geomagic Studio software, which was used to build digital models. L1 osteoporotic burst fracture and different posterior fixation techniques were simulated by SolidWorks software. The data of ROM, the maximum displacement of fixed segment, ROM of fractured L1 vertebrae, the stress on the screws and rods as well as on fractured L1 vertebrae under different movement conditions were collected and analysed by finite element analysis.Results: Among the four groups, the largest ROM of fixed segment, the maximum displacement of fixed segment and ROM of fractured vertebrae occurred in CBT, and the corresponding data was 1.3°, 2.57 mm and 1.37°, respectively. While the smallest ROM of fixed segment, the maximum displacement of fixed segment and ROM of fractured vertebrae was found in LSPS, and the corresponding data was 0.92°, 2.46 mm and 0.89°, respectively. The largest stress of screws was 390.97 Mpa, appeared in CBT, and the largest stress of rods was 84.68 MPa, appeared in LSPS. The stress concentrated at the junction area between the root screws and rods. The maximum stress on fractured vertebrae was 93.25 MPa, appeared in CBT and the minimum stress was 56.68 MPa, appeared in CAPS. And the stress of fractured vertebrae concentrated in the middle and posterior column of the fixed segment, especially in the posterior edge of the superior endplate.Conclusion: In this study, long-segment posterior fixation (LSPF) provided with the greatest stability of fixed segment after fixation, while cortical bone screw fixation (CBT) provided with the smallest stability. Cement-augmented pedicle screw-rod fixation (CAPS) and combined using cortical bone screw and pedicle screw fixation (CBT-PS) provided with the moderate stability. CBT-PS exhibited superiority in resistance of rotational torsion for using multiple connecting rods. CAPS and CBT-PS maybe biomechanically superior options for the surgical treatment of burst TL fractures in osteoporotic patients

Simultaneous calibration: a joint optimization approach for multiple Kinect and external cameras

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